1. Field of the Invention
This invention relates to artificial mineral fibers or whiskers having excellent heat insulating properties, heat resistance, fire resistance, and chemical resistance, and processes for preparing the same. More particularly, this invention relates to a novel fibrous potassium titanate having a noncrystalline or amorphous structure and a simple process for preparing the said titanate fibers in which a mixture of potassium compound(s) and titanium compound(s) is kneaded and calcined.
2. Description of the Prior Art
Fibrous potassium titanates have long attracted attention as artificial mineral fibers having excellent heat insulating properties, chemical resistance, and heat and fire resistance. The chemical composition of these products is represented by the general formula K.sub.2 O.nTiO.sub.2 wherein n has a value of 2.5 to 8. Among these products, fibrous potassium tetratitanate and potassium hexatitanate of the formulas K.sub.2 O.4TiO.sub.2 and K.sub.2 O.6TiO.sub.2, respectively, show particularly excellent heat insulation and heat, tire, and chemical resistance which makes them good thermo and chemical insulators.
We have investigated the hydrothermal synthesis of fibrous potassium titinates, see Yogyo-Kyokai-Shi, 76, 207 (1968). ibid., 83, 305(1975), the disclosure of which is herein incorporated by reference.
Several processes for preparing fibrous potassium titanates are known. U.S. Pat. No. 2,833,620, discloses a process which comprises reacting a potassium compound and a titanium compound in the presence of water at a temperature of at least 400.degree. C. under a pressure of at least 200 atmospheres. On the other hand, U.S. Pat. No. 2,841,470 discloses a process which comprises dissolving a non-fibrous potassium titanate in a fused alkali metal salt, maintaining a portion of the molten salt saturated with the dissolved compound to form the fibrous potassium titanate and then separating the crystallized titanate fibers from the salt by water extraction. Further, U.S. Pat. No. 3,328,117 discloses a method for producing a fibrous, water-insoluble alkali metal titanate which comprises calcining and reacting under essentially dry, non-fluid conditions a previously dry-blended nodular compacted mixture of an alkali metal compound with a titanium compound at a calcination temperature of 200.degree. to 1150.degree. C., leaching the thus obtained product to remove undesired substances therefrom, and then filtering, exfoliating, drying, and recovering the desired fibrous alkali titanate product. However, according to all of the U.S. patents mentioned above, the fibrous products obtained were shown from the X-ray diffraction patterns thereof to possess crystalline structures. Furthermore, the fibers of potassium titanate disclosed in the specifications of these U.S. patents are relatively short and the ratio of length to diameter of the fibers is low. Hence, these fibrous products still can not be made into paper-like articles utilizing water collection processes such as that used in the manufacturing of paper.